342 
COMPARATIVE ZOOLOGY. 
1. Monotremata. — This order includes two singular 
forms, the Duck-mole ( Ornithorhynchus) and Spiny Ant- 
eater {Echidna), both confined to the Australian conti¬ 
nent and New Guinea. The former has a covering of 
fur, a bill like that of a Duck, and webbed feet. The lat¬ 
ter is covered with spines, has a long, toothless snout, like 
the Ant-eater’s, and the feet are not webbed. Both bur- 
Fig. 331.—Ornithorhynchus. 
row, and feed upon Insects. The brain is smooth in the 
Ornithorhynchus, and folded in the Echidna. In both, 
the cerebral hemispheres are loosely united by transverse 
fibres, and do not cover the cerebellum and olfactory 
lobes. 176 Both lay eggs which resemble those of Birds and 
from which the young are hatched. 
Subclass II.— Dideiphia. 
In these implacental Mammals the uterus is divided 
into two parts. 
2. Marsupialia are distinguished by the fact that the 
young, always born premature, are transferred by the 
mother to a pouch on the abdomen, where they are at¬ 
tached to the nipples, and the milk is forced into their 
